Well production apparatus

ABSTRACT

A method and apparatus for producing a warm fluid from a well through casing, the casing passing through a permafrost zone, wherein the permafrost is insulated from melting by the combined use of vacuum and solid thermal insulation.

United States Patent 1151 3,680,631

Allen et a]. 1 51 Aug. 1, 1972 [54] WELL PRODUCTION APPARATUS 1,565,25412/1925 Bystrom, ..138/148X "um 2,451,146 10/1948 Baker etal ..138/149[72] i 3;, jft' 'f 35 3,142,336 7/1964 Doscher ..l66/57 x f 3,146,0058/1964 Peyton ..285/47 0 3,511,282 5/1970 Willhite etal .....166/303 x u2 3 gkhfield p y New 3,574,357 4/1971 Alexandru etal ..13s/149x or 22Filed: Oct. 2, 1970 A] k C I L Z Z F M w M as an omp etions i e ompicaten or [52] US. Cl ..l66/57, 166/DIG. 1, 166/242 Primary Examiner-StephenJ. Novosad [51] Int. Cl. ..E2lb 43/00 Attorney-Blucher S. Tharp andRoderick W. Mac- [58] Field of Search ..l66/302, 303, 57, 242, 243,Donald l66/DIG. 1; l38/l09, 113, 148, 149; 285/47 [57] ABSTRACT [56]References Cited A method and apparatus for producing a warm fluidUNITED STATES PATENTS from a well through casing, the casing passingthrough a permafrost zone, wherein the permafrost is insulated 3,380,5304/1968 McConnell etal ..l66/242X from melting by the combined use ofvacuum and 3,371,946 3/1968 Bleyleetal. ..13s/149x l-dth 3,275,3459/1966 Waldronetal. ..l38/148X msuam 1,218,895 3/1917 Porter ..138/148l8Claims,5DrawingFigures sci P'A'TENTEDAuc 1 I972 sum 1 or 2 FIG. I

FIG. 2

I N VEN TOR WILLIAM G. ALLEN JAMES A. Le VELLE FRANK J. SCHUH W M W'MPATENTEDms 1 I972 SHEET 2 0F 2 FIG. 5

WILLIAM G. ALLEN INVENTUR FIG.3

JAMES A. Let ELLE FRANK J. SCHUH ATTORNEY WELL PRODUCTION APPARATUSBACKGROUND OF THE INVENTION Heretofore in the production of warm fluidsuch as petroleum gas and/or petroleum liquid from a wellbore in theearth through a permafrost zone whereby part of the permafrost could bemelted upon continued exposure to the warm fluid, it has been proposedto coat or otherwise surround the casing or tubing (pipe) in thewellbore with solid thermal insulation such as polyurethane foam. Theinsulation normally extends from the earths surface down to the bottomof the permafrost zone in a continuous cylindrical form.

Thermal insulation applied in this manner to the outside of casing ortubing is expensive to apply to each joint of the pipe as it passes intothe wellbore because it takes up the time of the rig and the workmen toapply the insulation. The insulation is-quite fragile under the normalconditions in which pipe of any type is inserted into a wellbore and,therefore, is likely to be at least partially scraped or otherwisebroken off from the pipe before the pipe is set into its final positionin the wellbore. Further, some insulation, particularly the porous typeof insulation, does not act as efficiently in a wellbore if liquid,which is almost always present in a wellbore, penetrates the pores ofthe insulation.

Thus, it is highly desirable to have an efficient type of insulationwhich is quite durable under normal operating and pipe emplacementconditions on a well so that one can be certain that the insulation isintact when the pipe is emplaced in its final position in the wellboreand which does not take up an undue amount of time of the rig andpersonnel when running the pipe into the wellbore.

SUMMARY OF THE INVENTION According to this invention all of the aboverequirements are met by minimizing the amount of solid insulation usedand physically protecting the minor amount of solid insulation that isused.

According to this invention, apparatus wherein each section of casing,tubing, or other pipe which is desirably insulated in the permafrostzone of the wellbore, hereinafter referred to collectively as casing, isprovided with a vacuum chamber for substantially the complete length ofeach section of casing but which vacuum chamber terminates a finitedistance short of either end of each section of casing so that whensections of casing are joined one to another there is an area ofrelatively uninsulated space where the two sections of easing are joinedone to another. Solid insulation is employed in these relatively smalluninsulated spaces, and is protected by the configuration of the vacuumchamber itself or holding members or both.

This invention also relates to a method of producing a warm fluidthrough a casing zone in a wellbore in the earth, the wellbore passingthrough a zone of permafrost that can be melted in part upon continuedexposure to the warm fluid wherein there is provided a plurality ofspaced apart vacuum zones along the length of the casing zone in thepermafrost zone. There is thus established a plurality of vacuum zoneswherein each pair of adjacent vacuum zones has an uninsulated spacetherebetween and there is provided in at least one of these uninsulatedspaces a solid insulation material to provide substantially continuousinsulation of the vacuum or solid type throughout the permafrost zone.Thereafter the warm fluid is produced through the thus insulated casingzone to the earthssurface.

This invention provides a method and apparatus whereby fluids hot enoughto melt permafrost can be continuously produced through a permafrostzone for a long period of time such as 20 years without substantiallymelting the permafrostitself.

Accordingly, it is. an object of this inventionto provide a new andimproved method and apparatus for producing wells through a permafrostzone. It is another object to provide anew andimproved method andapparatus for thermally insulating pipe in a wellbore. It is anotherobject to provide a new and improved method and apparatus for producinghot fluid through permafrost without substantially melting thepermafrost. It is another object to provide a new and improved methodand apparatus for thermally insulating at least part of a wellbore in amanner wherein the insulation will stand up under normal handling andemplacement of casing and the like in the wellbore.

Other aspects, objects, and'advantages of this invention will beapparent to those skilled in-the art from this disclosure and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a cross-section of awellbore containing a permafrost zone and with casing emplaced thereinin accordance with this invention.

FIGS. 2 through 5 show cross-sections of various em-' bodiments withinthis invention for arranging the vacuum chambers, the solid insulationin the uninsulated areas where two sections of casing are joined, andvarious coupling means.

DETAILED DESCRIPTION OF THE INVENTION More specifically, FIG. 1 showsthe earth's surface 1 with a wellbore 2 drilled therein, the bottom ofthe wellbore not being shown for sake'of brevity. wellbore 2 passesthrough a tundra zone 3 at the earths surface which extends downwardly ashort distance of, for example, 2 feet to a permafrost zone 4. Belowzone 4 is unfrozen earth zone-5.

A casing string 6, which can be one or more strings of concentric pipe,is shown to be composed of, for simplicity, three individual sections ofcasing denoted by reference numerals 7, 8, and 9. Casing section 7, thetop of which is not shown, is fixed to a conventional wellhead (notshown) which is well known in the art and which extends downwardly intothe permafrost zone and terminates at joint line 10.

Casing section 8 starts at line 10 and extends downwardly to joint line11. Casing sections 7 and 8 contain annular vacuum chambers 12 and 13,respectively. These chambers terminate a finite distance from the endsof each section'so that, for example, when sections 7 and 8 are joinedas represented by line 10 there is a finite distance 14 of substantiallyuninsulated casing space. Uninsulated space 14 contains solidinsulation, as will be shown hereinafter in detail.

Casing sections 7 and 8 are joined to one another by each threading intoa conventional sleeve type coupling 15 which is well known in the art.Casing sections 8 and 9 are also joined at line 1 l by sleeve coupling16.

Casing section 9 starts at line 11 and extends downwardly out of thepermafrost zone 4 into the unfrozen zone 5 and there is cemented in byway of cement 17 so that it supports casing sections 7 and 8 and thewellhead.

FIG. 2 shows an enlarged cross-section of the bottom portion of casingsection 7 and an upper portion of casing section 8 including uninsulatedsection 14. Space 14 is shown in FIG. 2 to contain an annular, rightcylindrical section 20 of solid thermal insulation to providecontinuityof insulation from vacuum chamber 12 to vacuum chamber .13.

In FIG. 2 casing sections 7 and 8 are shown to have main walls 21 and22, respectively. Vacuum chambers 12 and 13 extend inwardly from mainwalls 21 and 22 g as provided by an inwardly extending annular ring 23which defines thelower end of chamber 12 and which has a matching member(not shown) enclosing the top of chamber 12. The inner surface ofchamber 12 is closed between the lower and upper annular rings by way ofannular, right cylindrical sleeve 24.

Sleeve 24 has an extension member 25 which extends from the lower end 23of vacuum chamber 12 towards the nearest end of easing section 7, i.e.,line 10. Member 25 is spaced inwardly from main wall 21 to provide aslot for insertion of insulation 20. This slot holds insulation 20 inplace and protects the insulation from material passing through theinterior of the casing. Depending upon the amount of protection desired,member 25 can extend substantially to line or any desired distance fromring 23 towards line 10.

Insulation 20 can extend into contact with either or both of rings23 and26. Alternatively an annular insulation material such as rubber can beinserted between insulation 20 and rings 23 and 26 as represented byannular .ringinserts 32 and 32'- Inserts 32 and 32' can provide a sealagainst thermal convection currents.

Vacuum chamber 13 is similarly configured with an inwardly extending,upper, annular ring 26 which is the same typeof ring which constitutesthe upper ring for chamber 12. Casing section 8 has a ring similar toring 23 (not shown) forming the bottom end of chamber 13 and these tworings are joined by inner sleeve 27 to define closed chamber 13. Ring 26has openable port 28 therein by means of which a vacuum can be pulled inthe interior of chamber 13. This is also true for the upper ring ofchamber 12. Inner sleeve 27 also has an extension member 29 whichprovides the same functions as described hereinabove for member 25.

It should be noted that insulation 20, instead of occupying only part ofthe lateral space between members 25 and 29 and main walls 21 and 22,respectively, can

be sized-to substantially completely fill this space.

Vacuum chambers 12 and 13 can be substantially vacant of any matter orcan have placed therein additional solid or. liquid thermal insulatingmaterial or other types of insulating material, such as radiantinsulating material, as desired. For example, one or more layers ofsolid insulating material can be emplaced in chambers 12 and 13 asrepresented by 30 and 31. This "additional-insulation at least partiallyfills the vacuum chambers: The one or more layers of insulating materialcan be alternated with thermal insulation and other types of insulationas desired.

FIG. 3 shows the joined area of two adjacent sections of casing such asthat shown in FIGS. 1 and 2 and as represented by upper and lower casingsections 33 and 34 joined at line 35 by conventional sleeve typecoupling 36.

However, one difierence in configuration in FIG. 3 is that main walls 37and 38'carry outwardly extending vacuum chambers 39 and 40 instead ofinwardly extending chambers 12 and 13 of FIGS. 1 and 2. Chambers 39 and40 can also be empty or contain one or more layers of solid and/orliquid insulation materials 41 and 42.

Chamber 39 is defined by an outwardly extending lower, annular, end ring43 which contains a vacuum port 44 and which before welding is integralonly with transition piece 37' of wall 37. Sleeve 45 extends from weld52 to a similar upper weld (not shown).

Member 46 extends downwardly from sleeve 45 towards the nearest end ofcasing section 33 to provide a holding and protection member for anannular, right cylindrical ring of solid insulation material 47.

Outwardly extending chamber 40 is composed of an upper annular ring 48which before welding is integral only with transition piece 38' of innersleeve 38, outer sleeve 49 being welded at the bottom of a weld similarto weld 52 to form the enclosed chamber 40. Ring 48 is substantially thesame as the upper ring which closes chamber 39. Extension member 50 isprovided in the same manner and for the same reasons as member 46. Hereagain members 46 and 50 can extend toward line 35 any desired length,depending upon the desired amount of protection for insulation 47 andthe ease with which insulation 47 can be put in place. It should benoted also that insulation 47 has a notched out'portion 51 whichaccommodates coupling 36.

FIG. 3 also shows welds 52 through 57, inclusive. This makes parts 45',37, 38", and 49' severablefrom the casing section walls 45, 37, 38, and49, respectively. Parts 45', 37, 38, and 49', are transition pieceswhich constitute a type of tool 'joint,'parts 45 and 49' being inaddition transition piece spacersdue to the spacing function of members43 and 48. 6

There are distinct advantages in the fabrication of the overall casingsection by having severable tool joints. In assembling casing section33, ,wall section 45 and 37 are initially separate and are composed of aconventional casing steel whose strength and other desirablemetallurgical characteristics deteriorate when exposed to extreme heatsuch as that encountered in welding operations. In the first step ofassembly pieces '45 and 37' are welded at 52 and 53 to 45 and 37,respectively, but are not yet welded at 54. Similar steps are taken atthe opposite end (not shown) of sec-' tion 33. After making welds 52 and53, the still separate sections 45 and 37 with transition pieces at bothends are both heat treated at both ends to restore the strength andother desired metallurgical characteristics to the portions of 45 and 37adversely affected by the heat of welding at 52 and 53. Thereafterinsulation 41 can be wrapped around the outside of 37 between ring 43and the opposing ring at'the opposite end of 37 (not shown but the sameas ring 48) if it is desiredto have additional insulation in chamber 39.Then separate subassemblies 45 and 37 with their transition pieces areassembled as shown in FIG. 3 and final weld 54 made, a similar finalweld such as 55 being made at the opposite end of 33. The metallurgicalcomposition of transition pieces 45 and 37 is chosen so thatdeterioration, if any, of strength or other desired properties broughtabout by the heat involved in making weld 54 does not fall below theminimum strength and other properties of walls 45 and 37. Insulation 41can be protected from the heat of final welds such as 54 by spacing theinsulation 41 away from the end rings such as 43, inserting insulationrings such as asbestos between insulation 41 and the end rings, and thelike.

It can be seen from the above that by use of severable, weldabletransition pieces of selected metallurgical composition the fabricationof each casing section can be greatly facilitated with adverse effect onthe strength etc. of the casing used in the fabrication operation. Thus,commercially available casing pipe can be used in making the casingsections of this invention.

FIG. 4 shows yet another embodiment within the scope of this inventionwherein upper and lower casing sections 60 and 61 are threadably joinedwith one another by means of a pin 62' and box means 63' in lieu of theseparate couplings or 36.

FIG. 4 shows internally extending, empty vacuum chambers 64 and 65.Chamber 64 is defined by a lower ring 66, with vacuum port 67, part oftransition piece 68', the top of chamber 64 being enclosed by a similarupper annular ring. It should be noted that the upper and lower annularrings can be substantially perpendicular to the main wall of the casingsection as shown in FIG. 2 or at any desired inclination such as thatshown in FIG. 4. Similarly, chamber 65 is defined by an upper annularring 69 an integral part of transition piece 70' and enclosed by meansof a lower annular ring similar to ring 66. Both sleeves 68 and 70 carryextension members 71 and 72 as means for protecting solid insulation 73and for holding that insulation in place.

FIG. 4 shows that pin and box type connections are amenable to the tooljoint welding fabrication procedure disclosed in FIG. 3. In FIG. 4 aconventional tool joint composed of transition pieces 62' and 63' iswelded to 62 and 63 with welds 74 and 78. Similarly, transition spacerpieces 68' and 70' are welded to 68 and 70 with welds 75 and 79. The twosubassemblies are welded to one another with final welds 76 and 77. Thesteps of fabrication are the same as explained for FIG. 3 in that heattreating after welding subassemblies such as at 74, 75, 78, and 79, etc.is carried out to restore strength etc. lost by the welding after whichthe subassemblies are joined with final welds such as 76 and 77 tocomplete the casing section with welding, without further heat treating,and without adversely reducing the physical properties of the transitionpieces below the same properties of 62, 68, 63, and 70.

FIG. 5 shows upper and lower casing sections 80 and 81 having pin andbox joinder members 82 and 83, respectively. Outer vacuum chambers 84and 85 are defined in the same manner as prior chambers, the bottomportion of chamber 84 being defined by an annular ring 86 extendinglaterally outward from the main wall of pin 82 and joined at its outerend to sleeve 87. Similar explanation applies to the upper portion ofchamber 85 with upper perpendicular ring 88 and sleeve 89. Theuninsulated space along members 82 and 83 between rings 86 and 88carries annular, right cylindrical insulation 90 having a cutout portion91 for members 82 and 83. Ring 88 has a vacuum port 96.

FIG. 5 shows that the outer walls 87 and 89 of chambers 84 and 85,respectively, can provide protection for insulation 90 so thatinsulation 90 can be glued, taped or otherwise attached to the casingsections without the use of extension members. The extension memberssuch as members 46 and 50 can be eliminated because of the protectivefunction of the outwardly extending vacuum chambers themselves.

An alternative holding member for insulation 90 or the insulation of anyof FIGS. 1 through 4, can be a metal sleeve around the periphery of 90and overlapping walls 87 and 89. In this manner a relatively fragileinsulation can be used for 90 and still not be damaged duringtransportation or emplacement. If it is desired to keep fluids from 90an outer heat shrinkable sleeve 101 of, for example, polyethylene orpolypropylene can be shrunk around the outside of insulation 90 or ametal sleeve surrounding 90.

One or more of the interior surfaces of the vacuum chambers can becoated with a gas diffusion barrier such as a plating of nickel orchromium or alloys thereof. This barrier prevents gas from diffusingthrough one or more of the walls of the vacuum chamber into itsevacuated interior. Gas diffusion into the interior of a vacuum chambercould reduce the magnitude of the vacuum in the chamber. Chambers 84shows a diffusion barrier 92 on all the interior surfaces thereof.Chamber 85 shows a diffusion barrier 93 on two of the three interiorsurfaces shown. All or any lesser number of interior surfaces can becoated with one or more diffusion barriers as desired.

If desired, a corrosion barrier such as stainless steel can be employedon the outside and/or inside surfaces of the casing section which willcontact packer fluids, cement, drilling mud, and the like to prevent,for example, corrosion of the casing and the formation of hydrogen whichmay diffuse into the vacuum chamber.

The apparatus shown in FIGS. 1 and 5 can be fabricated and welded in thesame manner disclosed for FIGS. 3 and 4, if desired.

The solid insulation employed in this invention in the interior of thevacuum chambers or the uninsulated space between adjacent casing sectioncan be any material which is substantially nonporous, or contains pores,bubbles, voids, and the like, or is composed of 2 or more separatelayers of materials, etc. By solid what is meant therefore is anyinsulating material which will maintain its shape although not confinedon all sides. This is shown in FIGS. 2 through 5 for insulation 20, 47,73, and 90. Suitable insulation include polymers such as polyvinylchloride, polyethylene, polypropylene, foamed polyethylene, foamedpolypropylene, nylon, polytetrafluoroethylene, polyurethane, asbestos,and the like.

Rings 23, 26, 43, 48, 66, 86, etc. and any other element which providesa path for heat flow around the vacuum chambers can be made of lowthermal conductivity metal such as certain stainless steels or even ofnonmetal thermal insulation or a combination thereof.

When the vacuum chambers extend inwardly from the main wall of thecasing section they can extend quite close to both ends of the casingsection although there is always some slight space where two adjacentsections of casing are joined in which space there is no vacuum chambercoverage. For this space there should be provided solid insulation asdisclosed hereinabove.

When the vacuum chambers extend on the outside of the main wall of thecasing section the ends of the vacuum chambers can not as closelyapproach the ends of the casing section as when the vacuum chambersextend inwardly from the main wall. This is so because in the normalhandling of casing for emplacement of same in the wellbore, varioustools such as slips, tongs, and the like are employed which grip theexternal surface of the casing-in a rough and forceful manner. In orderto prevent damage to the outwardly extending vacuum chambers, thesechambers terminate a finite distance from both ends of a given casingsection to provide an exposed length of main casing wall, such as length95 in FIG. 3, so that either end of the casing section can be graspedwith slips, and the like without damaging the external vacuum chamber.This requirement will have a limiting value on the length of extensionmembers 46 and 50. Thus, allowance should be made at both ends ofoutwardly extending vacuum chambers for the emplacement of working toolson the main wall of the casingsection adjacent both ends of thatsection.

if desired, conventional gas absorbing material sometimes called gettermaterials can be employed in the in terior of the vacuum chambers toabsorb any gas that may leak or difiuse into the vacuum chamber duringuse so that the magnitude of vacuum initially imposed upon that chambercan be substantially maintained. Any conventional getter can beemployed, e.g., PdO on a dessicant, molecular sieve, and the like.

According to the method of this invention, a warm fluid such aspetroleum gas and/or liquid which is at a temperature which can meltpermafrost upon continued exposure, i.e., at a temperature greater than32 F.. preferably at least about 100 F., is pumped from the bottom ofthe well to the earths surface through the casing, including that partof the casing that passes through the permafrost zone. The pumping canbe carried out for an extended length of time while the temperature atthepermafrost face 2 of the wellbore is no greater than 32 F., moregenerally in the range of from about 14 to about 32 F.

The improvement in this production method comprises providing aplurality of spaced apart vacuum zones such as zones 12 and 13 of FIG. 1along the length of the casing zone in the permafrost zone therebyestablishing a plurality of vacuum zones wherein each pair of adjacentvacuum zones has therebetween an uninsulated space such as area 14 ofFIG. I. Thereafter providing in at least one of these uninsulated spacesbetween adjacent vacuum zones a solid insulation material forsubstantially continuous insulation by either vacuum or solid insulationthroughout the length of thepermafrost zone, and producing the warmfluid through the casing zone to the earths surface.

t The vacuum employed can vary widely depending upon the desiredinsulating effect but will generally be in the range of from about 100to about preferably from about 10 to about 10', millimeters of mercury.

EXAMPLE between the 7 inch and 9 ii! inch casings, being the annularspace for vacuum chambers 64 and 65 is 1.835 inches. A vacuum of about10" millimeters of mercury is imposed in these chambers with only airremaining.

Solid insulation 73 is a right cylindrical block of solid polyvinylchloride having a wall thickness of about 1 inch and a height of about 4inches.

This apparatus is employed in a permafrost zone having a temperature atthe face of the permafrost in the wellbore in the range of 14 to 32F.Liquid petroleum oil at a temperature of about 160 F. is pumped throughthe interior of the 7 inch casing for at least 1 year withoutsubstantial melting of the permafrost face which is approximately 5inches from the 9 '96 inch casmg. I

Reasonable variations and modifications are possible within the scope ofthis disclosure without departing from the spirit and scope of thisinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In apparatus for producing warm fiuidfrom a well through a pluralityof sections of casing means which passes through a permafrost zone, theimprovement comprising means defining'a closed annular chamber along thelength of each section of casing in said permafrost zone and capable ofholding a vacuum therein,

said chamber terminatinga finite distance from either end of each casingsection toprovide an uninsulated space where one casing section isjoined to another, and solid thermal insulation means extending acrosssaid uninsulated spaces between the ends of adjacent vacuum chambers sothat said vacuum chambers serve as protective means for said insulation.

2. Apparatus according to claim 1 wherein said vacuum chambers containin their interiors at least one layer of solid thermal insulation.

3. Apparatus according to claim v1 wherein there is a main wall for eachcasing section and said vacuum chambers extend outwardly therefrom, saidvacuum chamber terminates a distance from either end of each casingsection which is sufficient to allow working tools to be applied to saidmain wall without damaging said vacuum chamber, and annular solidthermal insulation extending around the outsideof said main wall in saiduninsulated space where one casing section is joined to another.

4. Apparatus according to claim 3 wherein said vacuum chambers containin their interiors at least one layer of solid thermal insulation.

5. Apparatus according to claim 3 wherein said vacuum chambers containin their interiors at least one layer of a gas diffusion barrier on atleast one interior surface.

6. Apparatus according to claim 1 wherein there is a main wall for eachcasing section and said vacuum chamber extends inwardly therefrom,annular solid thermal insulation extends around the interior of saidmain wall in said uninsulated space where one casing section is joinedto another, and means for protecting and holding said solid insulationin place.

7. Apparatus according to claim 6 wherein said vacuum chambers containin their interiors at least one layer of solid thermal insulation.

8. Apparatus according to claim 6 wherein said means for holding saidsolid insulation in place cornprises at least one member extending fromthe end of each vacuum chamber toward the nearest end of casing section,said members being spaced inwardly from said main wall.

9. Apparatus according to claim 6 wherein said vacuum chambers containin their interiors at least one gas diffusion barrier on at least oneinterior surface.

10. Apparatus according to claim 6 wherein said vacuum chambers containin their interiors at least one layer of solid thermal insulation and atleast one gas diffusion barrier.

ll. Apparatus according to claim 1 wherein each of said casing sectionscomprise two concentric, spaced apart inner and outer sleeves whichdefine the inner and outer walls of said closed annular chamber, thefirst of said sleeves having fixed thereto at both ends a transitionpiece, an annular ring fixed to said first sleeve and having one edgeextending laterally from said first sleeve toward the second andopposing sleeve, the second of said sleeves having a transition piecefixed thereto at both ends, and said outer edge of said ring being fixedto the second sleeve.

12. Apparatus according to claim 11 wherein said second sleevetransition piece is threaded for attachment to another casing section.

13. Apparatus according to claim 11 wherein said outer sleeveconstitutes a portion of the main wall of the casing section, the firstof said sleeves is the inner sleeve and has fixed thereto at both ends atransition piece which has an integral annular ring, said ring havingits outer edge extending laterally from said inner sleeve toward thesecond and opposing sleeve, the second of said sleeves is the outersleeve and has a threaded transition piece fixed thereto at both ends,and said outer edge of said ring is fixed to said outer sleeve.

14. Apparatus according to claim 11 wherein said inner sleeveconstitutes a portion of the main wall of the casing section, the firstof said sleeves is the outer sleeve and has fixed thereto at both ends atransition piece which has an integral annular ring, said ring havingits outer edge extending laterally from said outer sleeve toward thesecond and opposing sleeve, the second of said sleeves is the innersleeve and has a threaded transition piece fixed thereto at both ends,and said outer edge of said ring is fixed to said outer sleeve.

15. Apparatus according to claim 1 wherein said vacuum chambers containin their interiors at least one gas diflusion barrier on at least oneinterior surface.

16. Apparatus according to claim 1 wherein said vacuum chambers containin their interiors at least one layer of solid thermal insulation and atleast one gas difiii fifimus for producing warm fluid from a wellthrough a plurality of sections of easing means which passes through apermafrost zone, the improvement comprising means defining a closedannular chamber along the length of each section of casing in saidpermafrost zone and capable of holding a vacuum therein, said chamberterminating a finite distance from either end of each casing section toprovide an uninsulated space where one casing section is joined toanother, solid thermal insulation means extending across saiduninsulated spaces, a main wall for each casing section, said vacuumchamber extending inwardly from said main wall, said solid thermalinsulation means being annular and extending around the interior of saidmain wall in said uninsulated space where one casing section is joinedto another, means for holding said solid insulation in place comprisingat least one member extending from the end of each vacuum chamber towardthe nearest end of the casing section, said members being spacedinwardly from said main wall, and an annular rubber insert between eachend of said annular solid insulation and the adjacent end of the vacuumchamber.

18. In apparatus for producing warm fluid from a well through aplurality of sectionsof casing means which passes through a permafrostzone, the improvement comprising means defining a closed annular chamberalong the length of each section of casing in said permafrost zone andcapable of holding a vacuum therein, said chamber terminating a finitedistance from either end of each casing section to provide anuninsulated space where one casing section is joined to another, solidthermal insulation means extending across said uninsulated spaces, saidclosed annular chamber being composed of two concentric spaced apartinner and outer sleeves, one of said sleeves constituting a portion ofthe main wall of the casing section, the first of said sleeves havingfixed thereto at both ends an elongated transition spacer piece with anintegral annular ring having its outer edge extending laterallytherefrom toward the second and opposing sleeve, the second of saidsleeves having a threaded spacer piece fixed thereto at both ends, saidouter edge of said ring being fixed to the second sleeve, and extensionmember means carried by at least one of said spacer pieces and extendsfrom the end of said spacer piece toward the nearest end of the casingsection and spaced from said second sleeve to provide a socket forholding and protecting solid insulation inserted therein.

1. In apparatus for producing warm fluid from a well through a pluralityof sections of casing means which passes through a permafrost zone, theimprovement comprising means defining a closed annular chamber along thelength of each section of casing in said permafrost zone and capable ofholding a vacuum therein, said chamber terminating a finite distancefrom either end of each casing section to provide an uninsulated spacewhere one casing section is joined to another, and solid thermalinsulation means extending across said uninsulated spaces between theends of adjacent vacuum chambers so that said vacuum chambers serve asprotective means for said insulation.
 2. Apparatus according to claim 1wherein said vacuum chambers contain in their interiors at least onelayer of solid thermal insulation.
 3. Apparatus according to claim 1wherein there is a main wall for each casing section and said vacuumchambers extend outwardly therefrom, said vacuum chamber terminates adistance from either end of each casing section which is sufficient toallow working tools to be applied to said main wall without damagingsaid vacuum chamber, and annular solid thermal insulation extendingaround the outside of said main wall in said uninsulated space where onecasing section is joined to another.
 4. Apparatus according to claim 3wherein said vacuum chambers contain in their interiors at least onelayer of solid thermal insulation.
 5. Apparatus according to claim 3wherein said vacuum chambers contain in their interiors at least onelayer of a gas diffusion barrier on at least one interior surface. 6.Apparatus according to claim 1 wherein there is a main wall for eachcasing section and said vacuum chamber extends inwardly therefrom,annular solid thermal insulation extends around the interior of saidmain wall in said uninsulated space where one casing section is joinedto another, and means for protecting and holding said solid insulationin place.
 7. Apparatus according to claim 6 wherein said vacuum chamberscontain in their interiors at least one layer of solid thermalinsulation.
 8. Apparatus according to claim 6 wherein said means forholding said solid insulation in place comprises at least one memberextending from the end of each vacuum chamber toward the nearest end ofcasing section, said members being spaced inwardly from said main wall.9. Apparatus according to claim 6 wherein said vacuum chambers containin their interiors at least one gas diffusion barrier on at least oneinterior surface.
 10. Apparatus according to claim 6 wherein said vacuumchambers contain in their interiors at least one layer of solid thermalinsulation and at least one gas diffusion barrier.
 11. Apparatusaccording to claim 1 wherein each of said casing sections comprise twoconcentric, spaced apart inner and outer sleeves which define the innerand outer walls of said closed annular chamber, the first of saidsleeves having fixed thereto at both ends a transition piece, an annularring fixed to said first sleeve and having one edge extending laterallyfrom said first sleeve toward the second and opposing sleeve, the secondof said sleeves having a transition piece fixed thereto at both ends,and said outer edge of said ring being fixed to the second sleeve. 12.Apparatus according to claim 11 wherein said second sleeve transitionpiece is threaded for attachment to another casing section. 13.Apparatus according to claim 11 wherein said outer sleeve constitutes aportion of the main wall of the casing section, the first of saidsleeves is the inner sleeve and has fixed thereto at both ends atransition piece which has an integral annular ring, said ring havingits outer edge extending laterally from said inner sleeve toward thesecond and opposing sleeve, the second of said sleeves is the outersleeve and has a threaded transition piece fixed thereto at both ends,and said outer edge of said ring is fixed to said outer sleeve. 14.Apparatus according to claim 11 wherein said inner sleeve constitutes aportion of the main wall of the casing section, the first of saidsleeves is the outer sleeve and has fixed thereto at both ends atransition piece which has an integral annular ring, said ring havingits outer edge extending laterally from said outer sleeve toward thesecond and opposing sleeve, the second of said sleeves is the innersleeve and has a threaded transition piece fixed thereto at both ends,and said outer edge of said ring is fixed to said outer sleeve. 15.Apparatus according to claim 1 wherein said vacuum chambers contain intheir interiors at least one gas diffusion barrier on at least oneinterior surface.
 16. Apparatus according to claim 1 wherein said vacuumchambers contain in their interiors at least one layer of solid thermalinsulation and at least one gas diffusion barrier.
 17. In apparatus forproducing warm fluid from a well through a plurality of sections ofcasing means which passes through a permafrost zone, the improvementcomprising means defining a closed annular chamber along the length ofeach section of casing in said permafrost zone and capable of holding avacuum therein, said chamber terminating a finite distance from eitherend of each casing section to provide an uninsulated space where onecasing section is joined to another, solid thermal insulation meansextending across said uninsulated spaces, a main wall for each casingsection, said vacuum chamber extending inwardly from said main wall,said solid thermal insulation means being annular and extending aroundthe interior of said main wall in said uninsulAted space where onecasing section is joined to another, means for holding said solidinsulation in place comprising at least one member extending from theend of each vacuum chamber toward the nearest end of the casing section,said members being spaced inwardly from said main wall, and an annularrubber insert between each end of said annular solid insulation and theadjacent end of the vacuum chamber.
 18. In apparatus for producing warmfluid from a well through a plurality of sections of casing means whichpasses through a permafrost zone, the improvement comprising meansdefining a closed annular chamber along the length of each section ofcasing in said permafrost zone and capable of holding a vacuum therein,said chamber terminating a finite distance from either end of eachcasing section to provide an uninsulated space where one casing sectionis joined to another, solid thermal insulation means extending acrosssaid uninsulated spaces, said closed annular chamber being composed oftwo concentric spaced apart inner and outer sleeves, one of said sleevesconstituting a portion of the main wall of the casing section, the firstof said sleeves having fixed thereto at both ends an elongatedtransition spacer piece with an integral annular ring having its outeredge extending laterally therefrom toward the second and opposingsleeve, the second of said sleeves having a threaded spacer piece fixedthereto at both ends, said outer edge of said ring being fixed to thesecond sleeve, and extension member means carried by at least one ofsaid spacer pieces and extends from the end of said spacer piece towardthe nearest end of the casing section and spaced from said second sleeveto provide a socket for holding and protecting solid insulation insertedtherein.